1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to an apparatus and method for measuring a received signal to interference ratio (SIR) for efficient, high-speed packet data transmission in a mobile communication system supporting a multimedia service including voice and data.
2. Description of the Related Art
Typical 3rd generation digital communication systems, particularly CDMA (Code Division Multiple Access) mobile communication systems, including IS-2000 and W-CDMA, support integrated transmission of voice, circuit data, and low rate packet data (e.g., packet data at or below 144 kbps). Along with the increasing demands for high rate packet data transmission like Internet browsing, mobile communication technology has been developed to support high rate packet data service. CDMA 2000 1×EV-DO (Evolution-Data Only) emerged to support a packet data service at a high rate, for example, at or above 2 Mbps. However, this system does not support a voice service. Therefore, there is a pressing need for a mobile communication system supporting the existing voice service and a high rate packet data service simultaneously.
One technique that satisfies the above demand and ensures efficient, high rate packet data transmission is AMC (Adaptive Modulation and Coding). In AMC, the fading of a radio channel is continuously monitored and data is transmitted at a data rate that ensures an error rate equal to or less than a threshold. An SIR measured in a mobile station is essential to measuring the radio channel status.
In general, a CDMA receiver is provided with a plurality of demodulation fingers to simultaneously demodulate signal components from multiple reflection paths, which are usually observed in a radio channel. Consequently, an SIR measurer is required for each demodulation finger. At a hard handoff from a radio channel to another radio channel, the mobile station must measure the SIRs of signals from base stations to which the hard handoff may occur (the base stations are managed as an active set) and thus have as many SIR measurers as the number of base stations.
Such an SIR measurer includes an F-PICH (Forward Pilot Channel) power measurer, an F-PDCH (Forward Packet Data Channel) power measurer, and a noise or interference power measurer.
The use of these complex SIR measurers is contradictory to the trend of terminal miniaturization and increases manufacture cost. Nevertheless, the SIR measuring technology is requisite for high rate packet transmission.
A mobile station utilizing AMC for efficient high rate packet transmission must measure the SIRs and packet channel power of base stations in its active set for a short time period, especially when power and orthogonal code resources assigned to packet data service users vary with the number of voice service users. Since a device for measuring the SIRs and packet power of signals from multiple reflection paths for all base stations is very complex, there is a pressing need for an accurate and less complex SIR measuring apparatus.